The present invention relates generally to controlled gas atmosphere enclosures. More particularly the present invention concerns such enclosures for laboratory use, such as the growth of biological cultures. The present invention relates particularly to rapid gas recovery methods and apparatus in an incubator system.
There are a number of commercial applications for controlled gas atmosphere enclosures. For example, electrical components and circuits are often tested in enclosures at a selected temperature and/or relative humidity for a period of time. Another common application for controlled atmosphere enclosures is the growth of biological cultures in the laboratory. As will be discussed herein with regard to a particular embodiment, the present invention may be advantageously employed in connection with a controlled gas atmosphere incubator in which a chamber for biological cultures is heated and in which the atmosphere of the chamber is controlled as to one or more constituent gases and/or the relative humidity.
A typical incubator of the foregoing type includes a generally cubical outer housing made up of five insulated walls (top, bottom, left side, right side, and rear) and an insulated front door. The door is mounted on hinges on the front of one of the side walls and may be opened to permit access to the interior of the incubator. When the door is closed, it is suitably sealed about its periphery to the housing walls to form the sixth wall of the housing. The incubator chamber, in which biological cultures are grown, is formed by inner walls, inside the insulated outer walls, and typically includes shelves upon which culture containers are placed. The shelves are carried by suitable shelf supports inside the chamber.
Most incubators of this type are either water jacket incubators or forced draft incubators. In a water jacket incubator the inner chamber is heated to the desired temperature by a sealed jacket of water surrounding the five fixed sides of the incubator chamber. The water jacket lies between the chamber wall and the insulated housing walls and is heated by heating elements in thermal contact with the water in the water jacket. Due to the thermal conductivity of water, the heat from the individual heating elements is relatively evenly dispersed over the water in the water jacket, providing even heating of the chamber. Such even heating is desirable in order to provide a uniform temperature for the biological cultures in different areas within the chamber and in order to prevent xe2x80x9ccold spotsxe2x80x9d on the inner chamber wall upon which condensation can form.
Although the heating of the chamber walls in a water jacket incubator is substantially uniform, the chamber atmosphere will stratify thermally if the chamber atmosphere is undisturbed. When such stratification occurs, the temperature of the chamber atmosphere is greater at the top of the chamber than at the bottom of the chamber. In addition, if a constituent gas concentration is maintained in the chamber, such as a particular CO2 level, the constituent gas will also stratify within the chamber atmosphere. Consequently, it is desirable to maintain a certain rate of flow within the chamber to assure uniformity of temperature and of constituent gases. In order to do this, typically a portion of the chamber is separated from the main chamber area by a wall to define a duct extending, for example, along a side of the chamber. A small blower or fan is placed in the duct and the chamber atmosphere is circulated, such as from a duct inlet in the upper portion of the chamber to a duct outlet in a lower portion of the chamber.
In a forced draft incubator, the inner chamber walls are insulated from the outer housing walls by a layer of insulation inside the housing walls. However, in this case there is no water jacket interposed between the insulated outer walls and the inner chamber walls. To obtain heating of the chamber in a forced draft incubator, some type of duct, such as described above, is typically provided within the chamber, and a fan and a heating element are mounted in the duct. As the fan circulates air from the main chamber area through the duct, the circulated chamber atmosphere is heated by the heating element. In order to heat the chamber atmosphere substantially uniformly, and to the desired temperature, considerably greater air flow is required than in the case of a water jacket incubator.
In a typical forced draft incubator, or water jacket incubator, if a constituent gas in the atmosphere of the incubator chamber is to be maintained at a particular level, a probe is introduced into the chamber, perhaps within the duct through which the chamber atmosphere circulates. In the case of CO2, for example, a CO2 sensor is introduced into the incubator chamber to measure the concentration of CO2 therein. A source of CO2 is then coupled to the interior of the chamber through a controlled valve, with an automatic control system actuating the valve as required to maintain the CO2 concentration in the chamber at a selected level.
The humidity in a forced draft incubator is also often controlled. Rather than introducing steam or water into the incubator chamber as may be done in the case of a water jacket incubator, in a forced draft incubator quite often a pan of water is placed upon the floor of the incubator chamber, and the recirculated chamber atmosphere is directed out of the bottom of a duct across the surface of the water in the pan. Due to the higher recirculation rates in a forced draft incubator, appropriate humidification of the chamber is obtained.
In either a forced draft or a water jacket incubator, sensors such as for CO2 or humidity have typically been located within the chamber atmosphere itself, although perhaps within a recirculation duct, as earlier described. Such sensors in the chamber are subject to the chamber atmosphere, and a sensor can fail or suffer performance degradations due to contaminants or the accumulation of a coating on the sensor. The presence of such sensors in the incubator chamber itself also makes cleaning of the chamber interior more difficult. In fact, the very existence of a duct or the like for the circulation of the chamber atmosphere within the chamber introduces difficulties in cleaning the chamber.
The recirculation of the chamber atmosphere, such as through a duct, in either type of incubator presents yet another problem, that of potential contamination of biological cultures within the chamber. Contaminants such as mold spores are almost invariably present in the chamber atmosphere and may be directed by the recirculatory air flow into the biological culture containers. Culture contamination problems are exacerbated by the higher air flows required in forced draft incubators.
Higher air flow rates involved in forced draft incubators have a further disadvantage in that the higher flow rates tend to dry out biological culture media. To a large degree, the necessity of offsetting this desiccation results in the requirement for humidity control in forced draft incubators. In such incubators, a relatively high humidity is maintained so that the drying effect of the gas flow is ameliorated.
Incubators are typically used for growing cultures in a controlled environment wherein both temperature and atmospheric gas concentration are maintained at selected levels. For certain applications it is highly desirable to have both temperature and gas concentrations maintained within strict tolerances while still allowing easy access to the incubator chamber for adding or removing items to and from the chamber or for inspecting the contents of the chamber. Control of environmental variables is desirable to maintain accuracy and reproducability of incubation results.
Therefore, it would be desirable to provide an incubator having accurate gas concentration control with fast recovery of gases (typically CO2 combined with O2 or N2) by determination of the total gas volume required including gas loss due to same gas injection and gas loss due to other gas injection.
The foregoing needs have been satisfied to a great extent by the present invention which, in one aspect, includes the formulation of algorithms utilized for gas control in an incubator system. The algorithms are included in the firmware for an embedded controller and operate gas solenoids that have inputs defined as specific gases (e.g., CO2 alone or in combination with O2 or N2) at a defined pressure. The flow rate is then estimated and the needed volume for a specific gas is determined by numerically solving for the time the solenoid should be on. The algorithm adjusts for sensor response time and then a steady state algorithm ensues to bring the gas level to the final desired level and maintain gas levels due to normal loss.
It is accordingly an object of the present invention to provide an improved incubator control system which accurately maintains environmental levels within an incubator chamber.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.